1. Field of the Invention
The invention relates to a technical field of control devices and control methods for vehicles that can perform driver assisted control of various types, such as Lane Keeping Assist (LKA) in a vehicle equipped with various steering assisted devices such as Electronic controlled Power Steering (EPS), Variable Gear Ratio Steering (VGRS), and Active Rear Steering (ARS).
2. Description of Related Art
The device of such kind that causes the vehicle to perform lane keeping travel by using an electric power steering device and a steering angle variation device has been suggested (see, for example, Japanese Patent Application Publication No. 2007-160998 (JP-A-2007460998)). With the steering control device for a vehicle disclosed in JP-A-2007460998, the electric power steering device is controlled so as to obtain the target steering angle based on the curvature radius during lane keeping travel and the shift of vehicle position in the transverse direction with respect to the lane or the yaw angle is controlled by the steering angle variation device, thereby making it possible to keep the vehicle effectively within the target lane.
Setting a target steering angle Δδt on the basis of the target steering angle Δδt1 for keeping the Vehicle within the target lane and the target steering angle Δδts for bringing the vehicle behavior close to the standard state is also conventional (see, for example, Japanese Patent Application Publication No. 2006443101 (JP-A-2006-143101)).
When the vehicle is kept within the target lane by the steering angle control of turning wheels, the turning wheels that are the objects of steering angle control may be steered wheels (wheels coupled to the steering device, preferably front wheels) or non-steered wheels, and steering reaction torques of various kinds are generated in the steering device mechanically coupled to the steered wheels (this is a general concept of devices that transmit a steering input to steered wheels, these devices including various steering input devices such as a steering transmission mechanism, various steering shafts, and a steering wheel).
Since the steering reaction torque acts in the direction of interfering with the desired steering angle variation, the vehicle behavior will be disturbed, for example, by steering with the steering input device in the opposite steering direction, and keeping the vehicle within the target lane can be difficult, unless certain measures are taken against such steering reaction torque.
In the device disclosed in JP-A-2007-160998, although a plurality of steering devices, namely, an electric power steering device and a steering angle variation device are used, each device is merely individually responsible for part of the control relating to lane keeping and therefore the effect of such steering reaction torque is difficult to eliminate. Therefore, in actual operation, the driver should supply to the steering device a steering maintaining torque that acts against such steering reaction torque, and the so-called hands-free operation is difficult to realize.
In particular, the steering maintaining torque that is necessary when the driver maintains the steering of the steering input device changes in response to the steering reaction torque that varies regardless of the driver's intensions. Therefore, when the driver provides the steering maintaining torque via the steering input device, it is practically close to impossible to eliminate the possibility of the driver getting uncomfortable and the decrease in drivability is difficult to avoid.
Thus, with the device disclosed in JP-A-2007-160998, the decrease in drivability is difficult to avoid when the vehicle is kept within the target lane. The same is true for JP-A-2006443101 that neither discloses nor suggests the steering reaction torque.